Studies of Fe–Co based perovskite cathodes with different A-site cations

Iron–cobalt based perovskite cathodes with different A-site cations ((Ln 0.6Sr 0.4) 0.99Fe 0.8Co 0.2O 3− δ , where Ln is La, Pr, Sm or Gd) have been synthesised, characterised by a powder XRD, dilatometry, 4-point DC conductivity measurements, and electrochemical impedance spectroscopy (EIS) on cone shaped electrodes. In addition to this scanning electron microscopy (SEM) was used to characterise the bars. XRD revealed that only the La-containing perovskite was hexagonal. The Pr and Sm perovskites were orthorhombic. The gadolinium-based perovskite was a two phase system consisting of an orthorhombic and a cubic perovskite phase. The thermal expansion coefficient (TEC) increased systematically with a decrease in the size of the A-site cation until the gadolinium-containing perovskite where the TEC decreases abruptly. The total electric conductivity was the highest for the La-based perovskite and the lowest for the Gd-based perovskite as determined by 4-point DC conductivity measurements on bars. A clear correlation between the size of the A-site cation and the electrochemical performance was revealed, as the area specific resistance (ASR) was the lowest for the compounds with the smallest A-site cation. This might be explained on the background of the creation of a two-phase structure with a unique microstructure when the size of the A-site cation is lowered, or that one of the phases has a high electro-catalytic activity towards the electrochemical reduction of oxygen.